Unsure What's Wrong With My Camry :(

[GTrain]

Hey guys,

Kinda new around these boards and not too sure where to post my question, so sorry if its on the wrong board.

I own a 1997 Toyota Camry CSI. Its the 2.2L, 4 cylinder variant, 5 speed manual and has clocked 102,000 km. Its in pretty good condition(ie. I don't thrash my ride around or anything) and from a basic look-over, everything seems to be fine.

However, the last 3 days I've noticed that something's changed. Although when I start the car and drive everything's ok, after about 10-15 minutes of driving, I notice that there's a rumbling when I hit 2000-2400 RPM. The back window shakes enough to blur my vision when trying to look back and generally everybody in the car can feel the rumbling. Doesn't matter what gear it is, whether 1st or 5th, once it hits the 2000 RPM mark, the rumbling starts up again. It almost feels like I got one of those big mufflers, but on the inside of the car(if that makes sense)

Suggestions? Advice? Anything?

Thanks in advanced.