Any ideas what this engine sound is? (video)

[DennisG01]

I've had this sound for some time, now (a year or two). It has not gotten worse or changed in any way. I realize trying to diagnose things via a forum, even with a video, can be tough. But if anyone has any insight, that would be much appreciated. The sound ONLY happens once the engine gets good and warm, allowing the idle RPM's to come down. The sound ONLY happens at a dead idle - if I advance the throttle the tiniest bit, the sound goes away and the engine turns back to being silky smooth. The sound is the light rattling sound that you can (hopefully) hear in this video.

It seems to go away a little bit if I put pressure on the intake manifold. Note that it seems to go away even more in the video, but that is because my arm is possibly blocking some of the sound.

[JimLev]

Could be a number of things, noisy idler pulleys, water pump bearing, alternator bearings, PS pump, AC compressor.
The sound didn't change much when you touched the intake.
Take the belts off and spin everything by hand or get a stethoscope and listen to each one of the above.

[philly98540]

Maybe DISA valve

[Gumbi4u]

That chirping/squealing noise is guaranteed to be an idler pulley.

[DennisG01]

Wow, you guys are quick! Thank you.

I know it's hard to hear in the video, but if you can make it out, listen closely with the second placement of my hand. I was able to apply a little more pressure there.

I forgot to mention that I did go around with a stethoscope - but I will do it again. I 'thought' the noise might be coming from the area behind the oil filter when I did that? I'll check pulleys again, just to be sure, though.

I have no idea what the DISA valve is... but boy, 'google' in wonderful, isn't it? Now I do! Is it located in the center of the intake manifold? I wasn't quite sure after googling.

- - - Updated - - -

I looked around on this site for a DIY or a thread pertaining to the DISA, but couldn't find it. Did I miss it? The only threads I found were in the classified section.

- - - Updated - - -

I found some you-tubes that show the DISA. Seems easy enough to check. If there's any words of wisdom on this, feel free to blast away!

[EricP]

Your 97 doesn't have a DISA valve that I know of You have the regular M52 (non-TU) with only the 1 set of intake runners. The DISA valve is a flapper between a low and high RPM set of intake runners on the M52TU, M54, etc and would be present 99+ in E39's AFAIK.

The sound is likely resonating through the intake manifold, you might try a stethoscope type device to narrow down the location.. but that does sound like it could easily be an idler pulley somewhere. Could also be alternator, PS pump, water pump... blah blah. I'm not sure how ill-advised it is, but you could try running the engine for a very short period of time with no main accessory drive belt and see if the sound is completely gone, then you know 100% for sure it is an accessory. The scary thing in finding it though since it only occurs on a hot engine would be removing the belt powering the water pump.. maybe you could start by just spinning the accessories by hand on a warm engine after you shut it off when it has been making the noise.

It's also pretty reminscent of VANOS rattle, which would sound something like marbles in a can.

[JimLev]

No problem running it for a minute with the belts off.
If your concerned about doing this you and set the cabin heat and blower speed to max, should be good for a few minutes then.
Just keep an eye on the temp gauge and you'll be OK.

[DennisG01]

Well crap, I was 'hoping' for a dirty DISA butterfly valve! I pretty sure my engine is just a M52 - it's also a very early '97 with a March '96 build date.

Yes, I'm good with taking the belts off - I've done that with boat engines many times to diagnose exactly what you guys are referencing with bearings. Silly me, though, I didn't even think of that!

I was hoping the 'VANOS' thing wouldn't pop up... That one has me a little worried.

[EricP]

No problem running it for a minute with the belts off.
If your concerned about doing this you and set the cabin heat and blower speed to max, should be good for a few minutes then.
Just keep an eye on the temp gauge and you'll be OK.

Good idear

[plmadding01e39]

Sounds like a belt tensioner to me. My 530 made a noise just like that and I found that the source of the aggravating noise was a belt tensioner.

[DennisG01]

I could of sworn it was going to be something other than a pulley - considering that I was hearing the noise most prominently (through stethoscope) about 6"+ aft of the idler pulley. But just to do a quick double check, on your guy's recommendations, I sprayed a little WD-40 on the idler pulley as the engine was running and... the noise disappeared! Problem solved and will replace the pulley. Thanks for the guidance!

[edjack]

I would't drive it until you replace the pulley; it sounds that bad.

[DennisG01]

I think it sounds worse in the video - especially since even just the slightest bit of throttle (50 RPM's is more than enough) completely quiets it down to non-existant (not even detectable with a stethoscope). However, I already ordered the part last night so I'll be swapping it out early next week. But, thank you, I do appreciate the words of caution.

[BimmerBreaker]

That chirping/squealing noise is guaranteed to be an idler pulley.

+1

Replace the idler pulley and the belts

[Mannyf540]

To me it sounds like it's coming from the oil filter housing.

[DennisG01]

To me it sounds like it's coming from the oil filter housing.

That's what was throwing me off, too. The sound was louder down in that "valley" area between the oil filter housing and engine. But I guess it was just the way that the sound was travelling. Considering the WD-40 took away the noise immediately, it's a pretty safe bet the culprit is the idler pulley.