The empeg is working fine in the car. However, the last couple of times I've tried to plug it in indoors, the empeg doesn't power up, I get a rapid, constant clicking noise coming from my speakers and also from the small box located a couple of inches down the power lead from the input jack. I looked in the FAQ but couldn't see anything that covers this - anybody familiar with this one? It doesn't happen every time, which makes it hard to figure out! Is it safe to continue plugging in the empeg?