HTC One M9 - Reception & Call quality problems.

My problem:

- Sometimes I do not get call reception in my home (people call me but I do not hear the phone ring)

- When I do talk to people on the phone in my home sometimes they say my voice comes off 'muffled'...not clear.

- However, when they tell me my voice is muffled....I still hear them perfectly.

What I've done to try to fix:

- New SIM card

- Various factory resets

- ****My HTC Desire 530 has NO issues in the same conditions in my home.***

- Talked to my cell phone provider already. Again, my HTC Desire has no issues in my home.

Questions:

1. Can a faulty antenna be the cause of a person hearing me as muffled .....while me still hearing them perfectly?

2. Could this be both an antenna and a microphone issue?

Any suggestions, advice? Thank you