Strange Whistling Noise At High Revs

[itsmeself]

Hi guys,

I was hoping maybe someone here could help me out. I have recently bought an 06 diesel mondeo (6speed one) and i have just recently noticed a strange noise when accelerating in low gears. The noise is hard to describe really but the closest i can think to say is that it is like a whistle or whirring noise. A friend tells me it sounds like a noise he had in his old punto before the gearbox gave up on it, and after he told me that i did realise that on occasion it can be difficult to get it into 1st or 2nd gear). My questions are, does this sound like it might be a gearbox issue are there any ways i can easily check this and if it was a gearbox problem are they a major cost to replace/fix?

Thanks in advance for your help.

Conor