Noise after throttle repair and belt replacement...ideas?

[sirmalloc]

After my EML/DSC issues were resolved, I started noticing a pronounced low rumble slightly above idle and up to about 2500rpm. It's especially annoying when driving slowly around a parking lot.

The repair replaced the throttle actuator, and at the same time I had the dealer replace my alternator and A/C drive belts due to cracking. I took it back to the dealer and their tech took a listen and told me it was a Vanos noise, and I shouldn't be concerned. However, the noise starts at about 1000RPM, and it never happened before the repair, so I doubt it's Vanos.

Does anybody have any ideas or anything I can ask the dealer to check? Would an improperly tensioned belt cause this? Could it have anything to do with the new throttle actuator?