Torbeck valve in main water tank "pneumatic" when refills after toilet flus?

I wonder if someone could help with this problem. I replaced a side entry Torbeck valve on my main water tank in the loft as the old one was leaking.
However, with the new valve when I flush the toilet there is a "pneumatic drill" sound from the new valve in the loft when at the end of the tank fill. This does not seem to occur when I run the shower or the cold tap in the bathroom. I`ve changed the inhibitor from LP to HP but still the same. If I removed the pressure inhibitor to see if this resolves the issue would this be safe. The original Torbeck had the LP inhibitor.
Could the Torbeck be faulty ?
Thanks

RADAR
April 2009