We have a customer that has been experiencing audio quality issues with SPA303 phones. These SPA303 phones are not connected to a UC300 or UC500 system. The problem only occurs with the audio coming into the phones and does not occur with the audio coming out of the phones. The problem does not occur on every single call. This customer tells us that the audio cuts in and out during the calls that have the audio quality issue. These phones are running firmware release 7.4.9a. Is there an update that can fix this problem? We really need this problem fixed immediately.