Odd chirping noise from bellhousing

Strange. After replacing the flywheel ringgear and starter, and subsequently reinstalling the clutch, tranny and drive shaft, the starting problem is fixed, but now I have an annoying "chirping" noise coming from the bellhousing. At first startup it was constant, but after readjusting the clutch freeplay, it is now noticeable only when driving, and only on hard engine deceleration. Some times in second or third gear, as when slowing back down to come to a stop sigh, I let off the gas and let the engine braking slow the car. This is now the only time I hear the chirping, and it goes away if I push the clutch pedal in (towards the floor). At constant speed or accelerating, or at idle there is no noise.

Any ideas?

Thanks.

I didn't replace the throwout bearing, it only has about 100 miles on it and seemed in good shape. Since I last posted, I've readjusted the clutch free play and driven the car some, and the chirping noise has subsided. If it comes back, I'll pull the tranny again and investigate the input shaft shimming suggestion. Thanks.