It sounds like your mechanic didn't think it was significant, so don't obsess over it. Just move forward with your plans. If it breaks down the road, fix it then.When I had my headers and clutch installed I let the mechanic know to give it a listen when it was cold and he said he listened around and said it sounds like it's coming from the motor, but he couldn't quite figure out what it was and just told me not to worry about it lol. Hes done pretty much all the work on this car short of the cosmetic stuff the intake and the suspension. Hes even the one who did the opg's and has a 14 gt himself. I should of told him to pull the stretchy belt off while he was listening. I personally dont think its the stretchy belt off though because I'd think the noise would change while messing with the HVAC controls.
Anytime you do major performance upgrades like a blower, you should be ready to deal with consequences. Most of the time it works out well, but there is always a chance you will break the weak link in the chain so to speak. The possibility is ever present and goes with the territory.