GM-GMC: noise coming from bell housing, torque convertor, continuous pattern

Question
dont know what to check. kinda loud banging noise coming from bell housing, but in no continuous pattern, random and often, and only when at temp. doesnt do it at high speeds, just while idleing. sounds like head of bolt hitting something. first thing in morning when truck is first put in gear it jerks forward like being rearended. also when at temp and it is making the banging noise sometimes the engine, while idleing, will drop for a second when the noise hits.

Answer
Sounds to me like either your flywheel is cracked (not uncommon) or your torque convertor has come loose (never seen that).  Get a flash light and remove the inspection plate from the bell housing and have a look up inside, usually crack around the bolts in the centre.  The last possibility is internal engine problem, but not likely, it would be regular and at all engine speeds.  Have a look underneith and see what you can see.
Hope this helps