About a year ago, mine got weak and I was getting ready to order a new siren and did some debug first. The rain from the windshield runs down the right and left rear of the engine bay, there are drains in the well there and mine had leaves and dirt clogging them. This in turn caused water to backup and pool which pooled up to and around the siren which deadened the sound. Unclogged the drains and siren worked like a charm again. Did both sides, on the other side, it pools to the e box and that would not be pretty to get water in.

Easy to check the wells by removing black plastic trim with the 2 or 3 quarter turn fasteners at the rear of the engine bay.