A couple of months ago I purchased a Scorpion system for my '98 1.8Tqms. Great system, but I've noticed some peculiar behaviour a couple of times. For a few seconds, you can hear and feel a "rumbling" that is coming from around the down-pipe, or maybe farther into the exhaust. This rumbling stops when I get off the gas and comes back when I apply more throttle. After a few seconds I get a small back-fire and that's it. Now, here's more. This only happens when it is extremely wet, i.e. during heavy rain, AND when I' going on an overpass, or in a valley. So, the overpass and valley will have a rapid change in temperature, i.e. bidge ices first, type of thing. But, why is this happening at all? Does anyone have any ideas? The system works perfectly at any other time.<p>Marcin R.<br>---<br>'98.5 A4 1.8Tqms