Strange sound/feel from car

[LEVOC///MPower]

Thank you guys for all the inputs regarding the underdrive pulley.

What I recently found happening in my car but don't know if it is attributed to having underdrive crank pulley. The problem is this.
When the car is sitting at idle with engine running, I will periodically feel a thunk sound coming from what appears to be from the underneath the car. I can also feel this thunk as if someone had walked behind my car and kicked it.

This is very strange. this thunk comes about every minute or so as the car is sitting with engine at idle.

What could this be??? I certainly hope it isn't a symptom of a cracking crank shaft

[540Rob]

Mine does that sometimes when sitting in traffic but it is only when I go to put it into 1st.... In my case I think it is normal.

[540Rob]

Damn it... forgot to click the Email Notification...

[LEVOC///MPower]

Originally posted by 328isRob
Mine does that sometimes when sitting in traffic but it is only when I go to put it into 1st.... In my case I think it is normal.

What do you think is the cause of your thunking sound?

Why do you think it's normal?

[sammy328]

Mine makes the same thunk going into first too. I had a 944t that did the same thing... my mechanic told me it was perfectly normal and it was coming from the transmission tube/tranny (which was in the rear on the porsche) when i shifted into gear.

[540Rob]

I think the same thing but I never had a Porsche