Rubbing hissing noise near bottom bracket
I'm looking for a little bit of advice in troubleshooting an issue. I got a Trek5200 04' frame with Ultegra SL, Ksyrium wheels etc. Just recently when going down hill on semi rough roads I get some type of rubbing near the bottom bracket. The noise is like a hiss, but the vibration from some kind of rub travels up the seat tube. Noise and vibration goes away as I move the cranks forward. I've tried many times to see if the wheel is hitting something. I event did a complete overhaul of that entire section, remove BB, cranks, front derailleur, pedals, change cable, clean it up, and use grease when putting all screws back. I even check the area for cracks.
A mechanic did a quick check and didn't see anything. Reproducing the issue is difficult since I have to find a specific section that will allow the problem to occur. I was just wondering if anybody out there had experienced the same.
One thing I did due not too long ago was to cut my seat post, and one thing I haven't yet checked.