brake peddle releases air leak noise(above peddle)?
dont know much about volvo but if it has a brake booster it is probably bad, at least that is what it sounds like.
You need to change the brake booster. Mine have the same problem, but it fixed, after change the booster.
Search Volvo S90 Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Volvo S90 Experts