This is the issue. I started to notice it about 4 days ago and I don't know what is causing it. My engine is sounding like it's a diesel when I accelerate.

I did an oil flush and change last night, but that didn't help it (it may have made it a bit worse actually). I also added some Lucas Oil Stabilizer (about 1/4 of a 1L bottle) but that hasn't seemed to help. If I accelerate very slowly, the sound doesn't occur, but other than that it does. I'm afraid of what this could be... any thoughts? Thanks.