Connected to a UC540.
When external calls come in to a hunt group which the SPA525 is a member of, the phone rings, then rings again very quickly. Waits for a bit, then double rings again.. etc..
On an SPA504G on the same hunt group it rings normally.
Internal calls to this phone are fine.
It sounds as though the default ring tone for the SPA525 phones have been changed. The option to change this setting is on the phone itself, it the menus.
Check the ring settings for the phone. In CCA, user and extensions, choose that phone, then click on the main extension (Line 1), and on the right hand side, there will be a "ring parameters" tab. Under that tab, look at the "destictive ring" setting, and make sure it is set to "none".
Sorry, but I cannot think of anything else off the top of my head. It definitly sounds like a "distictive ring" issue on the phones, as a external call has a "double" ring. I would need to see the running configuration of the UC500 to look at all the settings. You may just want to open a case with TAC to have them take a look at everything also.
Go into the phones settings, and then reset the unit back to factory defaults, I would say it has reverted back to ITS defaults which often provides this double ring issue, it is not a cadence issue as the cadence Cisco uses is one Long tone or short burst tones, not double burst tones.
Also try it in another switch port just incase the phone is having issues in that particular port (Yes I know sounds crazy right, but believe me this has solved problems like this in the past)
One last thing to try, take it out of the blast group, reset the phone and then add it back into the blast group and see if that resolves the problem if the above two do not.
That's all I can think of for now... If that doesn't fix it, boat anchor time?