What could a dump valve noise be?

[WayneB73]

Hi all,

For a while now Iv had what sounds like a dump valve hissing noise under load and when changing gear. Van still seems to drive ok so just wondering what it could be?

The other question, had anyone ever used a tune up chip? Apparently it gives more Bhp, torque and better fuel economy, was wondering if this was a worthy upgrade ?

[dumper]

Check the boost pipes and intercooler get someone to rev the engine and squeeze the pipes on my brothers doblo it had oil weeping out of a split