bell housing

This hollow clanky sound just started Monday. You can hear it best when I switch over to the passenger side. Any idea what it might be?

I have up for sale a 03/04 T56 bell housing. I bought this to use with a terminator swap i'm doing on my 91 coupe but i ended up getting another one with a t56 i bought so i have no use for two of them. I de-greased and cleaned it up so it's ready to bolt on. I checked all the bolt holes and...