02 gp gt 200k miles

Car has a noise coming from the passenger side rear. Almost sounds like it's inside the trunk. Every time I hit a bump it makes a noise. It almost sounds like it's a hollow clunk. It's not a sharp popping type clunk like a front broken stabilizer bar makes. Car has been making this noise ever since I bought it a year ago. It's not a very loud noise but it's enough to wonder what's causing it. I never picked up on the sound until a month after I bought the car.

I checked rear seats, trunk, spare tire area. Strut towers look normal and there's no rust on them. Car drives straight down the road. No wobbles. The springs do sag a bit in the rear.

I'm aiming towards a possible bad strut mount. Are these hard to change out? I have all the tools except a spring compressor which I can probably rent. Autozone sells the mounts for $22 each.