Loss of fps due to Alt+Tab to join Mumble server?

[Eco__pRv]

Hey!

I realized a strange thing since I play 128/116 Sisu Server and use Mumble frequently. Start Mumble, connect - start PR, join server, check Squad leader names to find right team - Alt+Tab to Mumble to join correct team on the server. When I return to PR I have a terrible fps compared to before Alt+Tab or rounds that I start e.g. with having joined one team by chance or having mumble switched off (which is not really an option). Same problem seems to occur on other servers as well, but I haven't tested that extensively.

Can someone help or has any idea how to bypass this problem?

System:
Windows 7 Home Premium
Intel Core i5 450M
4GB RAM
ATI Mobility Radeon HD 5730