rotary

i just changed my rear tonight and im happy that everything is good again, but wtf is this weird sound i get in first gear. this is the sound that started all of my problems. here is the story.
about 2 months ago i started to get this funny sound from rite under my stick. it was moderate at first but it started to get worse with every time i went fast. then it started happening in 2nd gear about a week after the sound started. so i took it to my friends boss (who is the man with cars) and we put it up onthe lift. we found a couple of minor problems a one major one. he told me that i needed differential bushing (the lil bushings on top of the differential). he also said that i need a new lsd. i was skeptical about that and just got new bushings and a wheel bearing. i also bought a differential brace to stop the wheel hop i was getting and so i wouldnt blow my new bushings. right after i changed my bushings and put in my diff brace i go for a test drive i drop the clutch and boom. i have no more differential. this was about 3-4 weeks ago yesterday i went all the way to PA. for a differential. i put it in today and left the brace out, cause i was scared to put it in again. i took it for a test drive and what do i here when i go fast in first. yup the same sound that started this whole thing.
now let me tell you the the symptoms. it happens at just about when my boost kicks in at 4500 rpm in first gear and it only happens when i dump the gas. it dosent happen in neutral or in any other gear. but i bet if i keep driving it it will get worse. it sounds like buzzing or a vibrating or grinding. i was thinking about it today and it might be that i bent my power plant frame? i dont know but if anyone had this funny sound let me know what it is. thanx. this forum is the shizzznit