Low quality sound during call

Hello,

Since the iOS 7 update that I've been noticed that the sound quality during calls is very poor to others, almost like I speaking away from the iphone without speaker, regardeless I keep earing everything loud and clear!

I've already tested with other iphone 4/4S/5 iOS 7 users, and also running different iOS versions, as well as other phone brands, and the problem maintains!

Upgraded to 7.0.3 today, despite the improvement/enhancements/bug corrections list dont mention any issue addressed to this problem, hoping to solve the problem, but nothing change, its pretty much the same as before!

All settings are at the max, and also perform some tasks as suggested on apple support forums like tweaking the accessability options, by turning noise reduction off, but still the same!!

My S/N is C34JPLSTDTWF.

Hope I had described accuarately, in order to you perform the correct troubleshoot for this, this if you ain't already done it!

Best regards,

Pedro Sousa