Knocking noise!!

[milooo]

Hi guys, i have an awful knocking noise that seems to sound towards the middle front end where my feet area is. it is usually worse when at lower speeds and gets worse as i speed up then disappears at higher speeds. Also, the pointer on my rev counter looks like it struggling a bit as its sitting at about 500revs but when its cold it sits at about 1200. im so confused and its causing me a right headache!

I had the car dyno'd once again and it has lost 20hp. was at 173 now its at 152.

Could it be my exhaust? its took some beating

i heard something about a faulty knock sensor?

Please help as im selling it soon!

Thanks guys