Sounds pretty much normal Ops from any 206 that I've flown, I have 10,000 on type, mostly at altitude.
There is a procedure outlined in the Maintenance Manual to check for air leaks in the fuel system ...basically run the aircraft on the ground at 100% Nr for 2 minutes with BOTH boost pumps OFF (and at a low fuel quantity), the Eng driven pump sucks, so without boost pressure, it Will find any air-leaks ! This test should be done after any In-Tank maintenance.