e39 touring, strange audio problem

[danmurphymn]

I have a 2002 540iT. When I bought it a few months ago, it had no sound because the amp had gone bad. So I bought a new (used) DSP amp and now the music works. But it sounded like crap.
I just listen to podcasts, so I just played them through my phone instead of the stereo. But, the library finally got in the audiobook I've been waiting for! The subtle art of not giving a F*ck!

So I had to use the cd player. It sounds staticey, unclear but not horrible. So I figured maybe a speaker or something is blown. I also felt it was more centralized in the driver door.

Today on my way to work, I came to a stop and the audio was now clear. So I tested it out when I got to my office and yup, when I'm sitting still the audio seems clear. When I'm moving, it's junky.

Any thoughts on what's going on?

[MarcoZandrini]

Is the sound from all speakers affected?

[danmurphymn]

Is the sound from all speakers affected?

No, I don't think so. I feel like it's mostly just the driver door, maybe just the tweeter?
I haven't taken anything apart yet to look at wires etc. Just figured I'd ask in case there's some common issue with these.