Thumping when Shifting into 1st

Can't beleive how great this website is. ATTABOYS to everybody and whoever started it.

Anyway down to business. I have an 88 mustang with stock transmission and it seems more often then not when I shift into first from a stop I hear/feel a thump which seems like it is right under me. I have checked the u-joint and it doesn't seem loose. I have talked to people I trust and they don't think it is a big deal, but it just doesn't sound right. Anyway ideas?

Thanks!

Don't know to both Q's. First, I need to find out where the tranny mounting bolts are. Second "bellhousing" not sure what the heck that is. I have an idea but would probably sound more stupid trying to explain what I think it is then just pleading ignorance. Another question not sure how long this has been going on since the car is used, but could the long term effects of this be bad?

Thanks