Anyone using GrooVe IP with the One?

[yuiness]

I'm on Tmobile's $30/month 100min talk time plan, so I've been using GrooVe IP to make calls over wifi whenever possible. I've noticed that the speaker often makes crackling and popping sounds when the other party speaks loudly or holds his/her phone close to the receiver. I don't have any problems when using a headset, and normal (non-VOIP) voice calls don't seem to have this issue. I've admittedly never used GrooVe IP much before getting this phone, so I don't know if this is an issue with the app in general. Has anyone else encountered this? Any ideas on how to fix it? Is there something wrong with my top speaker?