Exhaust Tone

Hey guys, forester 2000 5 speed

Just some questions for exhaust gurus,

When I bought it I removed the stock silencer in the rear put a straight pipe to an exhaust tip and added a glass pack, sounded alright (Still have stock resonator also)

Then over the summer did a lot of long distance commutes with it and my "flex pipe" popped a hole through it so I replaced it with a straight pipe (Was way up north and all I found was some pipe and my cheap welder)

Alright so my question is this : When I give STRAIN on the engine (hard low RPM pull in 2nd or 3rd gear from 2000-3500 you hear sort of a rattle in the exhaust or underneath, would this be caused by the fact that my exhaust is pretty much all "Rigid" ? (It doesn't knock up against anything under the car to my knowledge)

My other question is at 120km/h there's a really bad frequency resonance in the car like droning, it only happens from 2900-3500 above that the exhaust is at a tone you can't hear inside, and below that also..

Any of you have experience with this to find a way to get the vibration at a certain RPM to be much lower inside the body, and would reinstalling a flexpipe help reduce vibration inside the car?

Thanks! May seem obvious to some of you but have a flexpipe installed or other exhaust work done here in the winter is pretty expensive, wanna make sure I'm going for the right shot!