1990 Accord EX-R

Over the past few months I've been experencing a loud noise coming from my engine whenever I accelerate. This only seams to happen when I'm in drive as I can rev it in park and it sounds okay. Its kinda hard to describe the noise itself, but its kind of like an exhaust leak without the low pitched sound of the pistons firing, Almost like a grinding sound. It doesn't seam to have an affect on my gas millage (then again I don't pay too much attention to that).

Any ideas?

 

I have a 2000 accord v6 ex and I'm hearing the same sounds as well. No grinding sound but you only hear it when accelerating. I have no clue what it is.