Rumbling sound when accelerating

Hello ya'll, I need some help diagnosing a sound that my 04' 2x4 eXtra is emitting from underneath the truck when never accelerating. I've searched through lots of other posts regarding similar sounds and symptoms but I'm just not 100% that it's the same issue cause I guess it doesn't really sound like anything is loose per say? And I don't think it's the cat either since I just had it smogged and it passed so if it were shot out then it wouldn't got certified right. Oh I almost forgot to mention my baby is pushing 300k but she still runs like a Champ everywhere else. I recently replaced the tie rods and ball joints and took it to a shop to have the alignment dialed and had them also check my double check my work, and I also replaced the AC compressor/condenser/dryer and the radiator but I know that none of my maintenance is the cause for the above mentioned sound because it was happening prior to all of that. I guess the noise could be described something more like a "purr" or "rumble" but not of the good sort if that makes any sense? Anyhow any perspective that could be contributed to my cause would be appreciated thanks fellow yota folk!

 

I have a 2011 pre-runner and have had the same issue for several months now.. took it in to the dealership they checked the exhaust system and changed the Universal joints and still didn't fix the noise that I hear when accelerating. They said just wait until it gets worse or whatever it is breaks!!really??? Somebody has to be having or had the same issue, if so please help me figure out the problem...thanks