Hi Jordan,
From a troubleshooting perspective - if you've recreated the problem on a 3745 as well as a 6608 blade, there's almost no chance the Cisco gear is causing the problem. Talk about apples and oranges.
Static is an analog/DSP caused problem. You should not be creating any on a PRI, and this doesn't sound like it's an issue on the DSPs since you've tested entirely different versions/hardware.
What is very possible is a certain channel on your PRI. Sometimes it's helpful to place a call, test the line, put it on hold, and try another. This fills up the PRI and allows you to test some of the channels that are not used until the PRI is filled up. You can also busy out channels or work with the provider.
Command for a non-mgcp controlled PRI:
interface serial 0/0:23
isdn busy b_channel
'show isdn service' tell you which ones you have busied out.
Cases like this can drag on, because we're fairly confident that problem is on the provider's side, but the provider will send a guy out, he'll make a couple test calls that sound good, and say it's a problem with your equipment.
The only time you should get static is when the RTP packet is created or modified, and generally that's only going to happen on your gateway and IP phones.
If you're working with TAC, you can get a PCM capture during the call to prove it's the provider.
hth,
nick