Knock noise

[pofire722]

Once I start my 07 Tundra 5.7, after it's been sitting for like a day or so, I hear a knock noise of some sort the second I turn on my air conditioning. It only knocks once and it sounds like it's coming from the drivers side engine area. It won't make the noise again unless the truck has been sitting for a day or so. My truck only has 2800 miles on it and it's basically been doing it right after I bought it. Any idea of what this might be, and does anyone else of the same issue?

[2008_CrewMax]

idk .. my truck makes weird noises from time to time too.

[Hawaii 5.7]

Originally Posted by pofire722

Once I start my 07 Tundra 5.7, after it's been sitting for like a day or so, I hear a knock noise of some sort the second I turn on my air conditioning. It only knocks once and it sounds like it's coming from the drivers side engine area. It won't make the noise again unless the truck has been sitting for a day or so. My truck only has 2800 miles on it and it's basically been doing it right after I bought it. Any idea of what this might be, and does anyone else of the same issue?

sounds like the a/c coming on!?!

Haven't noticed that sound, i'll pay attention next time i start truck.

[Smed]

Sounds like it may just be the clutch engaging the AC compressor. Has it changed? Did it not do this before?

[algolfer69]

Change the the positions on the A/C controller and listen for the sound. It may be a vent being pulled closed by vacuum, changing from outside air to recirculate.

[ramoine]

Welcome to the forum , sounds like the compressor .

[24hrtoy]

I've experienced a similar noise when troubleshooting another problem with hissing when I'm cruising. The knocking noise only happened once and haven't heard it again. Was coming from the top of engine under removable 5.7L cover..... weird!