I doubt the amp is just too much, but it is possible something is going on with them. I'd have it seen soon, to prevent damage to the speakers.
Visually inspect the woofers. With the amp off, check the dust caps and make sure they are still attached. Run your finger around the surround, make sure it's all in one piece, and finally, evenly, press the speaker in. It should move smoothly.
Visually inspect the woofers. With the amp off, check the dust caps and make sure they are still attached. Run your finger around the surround, make sure it's all in one piece, and finally, evenly, press the speaker in. It should move smoothly.