We had a similar problem in our Outback, especially when the air-conditioner runs. We solved the problem by getting a sound-bar. It worked so well, we ended up getting a Boise sound bar for the house living room. Granted the Boise cost a lot more and has a lot more UMPH! But the $125 one in the camper blasts the sound, especially with the wireless sub-woofer. Outside the camepr, you can here this "rumble, rumble, rumble". (and yes, we do usually turn the sub-woofer off at campgrounds, otherwise I think even the next camper to us would be vibrating!) They work really great! (Your television will need the fiber optic port though. The cheaper ones, don't have the old style red and white plug in jacks or even an earphone style jack either).
Got ours from Best Buy:
Click here.