Actually, depending on the condition of the vehicle, why not point out the noise and say not interested while it is present. They may offer to rectify for free. I wouldn't necessarily walk away unless it was a real HOS.
The condition of the vehicle inside & out is spotless.
When I viewed it - there was the noise and paperwork issues (no V5).
In the UK - you need a V5 form to tax the vehicle and become the registered keeper (different to the owner) to be able to put it on the road. You can make a request to the DVLA for a new V5 form in the buyers name - but it takes six+ weeks - in that time the vehicle cannot be used.
I asked for the included "oil service" to be removed from the price as the vehicle needs a Hyundai major service within 600miles and an amount off the vehicle list price to take the V5 paperwork delay into account. The dealer stopped communicating. I never got to talk about the noise.
I notice today that the price for the vehicle increased by £500...
Ho Hum - the search continues.