properly. "Carbon buildup on the valves" is not going to cause "rattling and squeaking" that you can hear in the cabin. Also, if the noise was not there before the tb work, but was there immediately after, it's not carbon buildup. First thing is to identify what noises started after the tb change, then insist the shop look at them. I've read some posts about the tb rubbing due to improper installation. ...... In general, it sounds like a clutch/driveline problem, except that you say it happened after tb work, and you are losing power. Maybe you have more than one problem. One would have to hear it to get a good opinion.