First off, yes I am a new member. Ok now to the question at hand.
I've had my 2000 Crown Vic LX for a few months now. Ever since I've purchased it I've only put about 6,000 miles on it, but when i took it out for a test drive on the interstate (I took it easy this for its first run) there was this odd rumble coming out of the rear end when I would go up hills with cruise control on at random intervals. At the time I didn't think much about it seeing as this section of the interstate is kinda bumpy. Well recently I'm becoming abit more concerned as its happening more frequently. Another friend of mine says it could be low fluid (but I haven't seen any leaks on the differential.) When I have the thing loaded down it doesn't do this (more people, gear, etc.). So any advice would be helpful. Thanks.