Wow.... this is a loaded question. IIRC, the '94 has an EGR valve and this could be something as simple as cleaning or replacing the valve. OTOH, it may be an intake gasket........ but without hearing the noise for myself, it's just too hard to say if there's a chance it may be something worse.
I would approach the current owner and express my desire to purchase the vehicle but that I wont as long as this particular noise is present. I would even go as far as offering to pay all or a portion of the repair if it doesn't exceed dollars..... IF this is the car I couldn't live without.
Having said that, I have seen these things go for years with noises - but that all depends on the noise. We also need to realize that this thing is ten years old, mileage unknown and area it lives in unknown. If all else fails, have a shop you trust take a look.... it might be money well spent.
HTH
-- Jim Warman snipped-for-privacy@telusplanet.net