KDub

I apologize if I'm breaking rules here. Brand new memeber.. just registered. Looking for advice on my 2011 Suburban LT, 4x4, 5.3 V8 aluminum block. Now has 150 k miles. I bought it brand new. No accidents. Treated like a baby. Regular service and replaced parts when needed.
Dealer replaced driver side engine mount 15k miles ago because loud "thump" on takeoff from standing start. I suggested he do the passenger side as well but he claimed it was fine. Recently (last 10k miles) I've heard and felt harsh engine noise and vibration. its getting worse. I bought GM passenger side engine mount and started to do it myself because I was convinced it was bad. But once I got to be able to see it, I found no signs of bad mount. No cracks. No leaking fluid. Ran a mirror around all 4 sides and ran finger all over it. It looks just fine and rubber feels soft like the new one. So now looking for other causes. It sounds/feels like the exhaust is contacting frame somewhere - but its not. Harsh engine noise at all speeds, except idle. Definately related to engine not suspension or transmission. Just loud general engine noise transmitted into cabin. Can feel it in pedals and steering.
What else may cause this? Anyone else had this problem? Possible that the passenger side engine mount has gone hard and brittle, but still looks OK? Hole in muffler on top where I cant see? Clogged cat converter? Rear transmission mount? ( its looks good).
Any suggestions would be much appreciated.
KDub