You know I have 2003 4.4i with 80K and i noticed some hissing noise, so I brought it in to a shop and they lifted it and we both looked, he says he doesn't see too many BMW's (The shop was Goodyear) but he said not to worry and keep driving it, but the noise came from above the transmission pan (the spot where you would drain and fill your trans fluid) the noise was like steam being released, not terribly loud but noticeable. There was a slight leak of tranny fluid and he tightened something and said that should help the leak. I wonder if I have low trans fluid that may cause it, he said not to worry and keep driving if it was him....I want to get a second opinion as well.

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2003 BMW E53 X5 4.4i - M62 engine (Non Sport with Premium and Cold Weather Package)
Color: Steel Gray Metallic
Mods:4.6is Exhaust (Pipes, Mufflers and chrome oval tips) BMW Sport package Taillamps, BMW Tire Valve Stem Caps
Medium tinted front windows
JVC HD Radio
Alpine 4x100 channel Amp
Orion 600W Mono HC Amp
Three 12" Sony Xplode in subwoofer enclosure