I own a 2004 Dodge Ram (5.7 L) ... 4X2. I am hearing some squeaking/rubbing type sound coming from underneath the truck near the rear axle. This sound begins as soon as you begin to accelerate. It continues as long as the truck is in motion (even at idle speeds). The sound speeds up as the truck accelerates. It even occurs while backing up. Once I get over 30+, I really can't hear the sound very well (too much background noise).

What does the sound sound like? It sounds like rubber squeaking/rubbing on something. It's not a metallic clanking sound. Any ideas?

I had my rear axle fluid changed by a quick lube place at 72 000 km as per the manual. Could they have forgotten to add the limited slip additive? Would that make that type of sound? The truck is nearing 80 000 km ... so would driving nearly 8000 km under normal driving conditions cause any damage to my LSD without the additive????

The sound is NOT coming from my tires/brakes ... I've checked that!