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Loud Static Noise on Call Transfers

We are having a problem where the calling party hears a loud static noise when transferred.  It occurs right after the transferring party hangs up.  You can hear the called party talking behind the static.  It lasts only for a couple of seconds.

Call comes in to operator ----> operator performs an announced transfer while caller hears music on hold ----> operator hangs up and call is transferred ----> Caller hears brief static at beginning of conversation.

The called party does not hear the static.

This happened with analog lines and SIP lines.

Anyone have a clue on this?

David Trad
Rising star

Hi Jason,

Standard questions just to get a mental image in my head

  • What Software Pack is being used on the system?
  • What Phone Load is being used on the phones?
  • Is it to all phones or only certain phones?
  • Does the static noise start of loud and then wane downwards or does it start soft and goes loud and then dissipates quickly?
  • Does it happen say when EXT-100 calls EXT-101 and then Transfers a call to EXT-102? Testing if it does it with On-net transfers
  • Does it happen when you make the call outbound and then transfer the call to someone else?

Sorry for all the questions this is just what i mull over in my mind when diagnosing a fault, sometimes for me working backwards can help out with narrowing down on the issue.



Cheers, David Trad. **When you rate a persons post, you are indicating a thank you or that it helped, but at the same time you are also helping to maintain the community spirit - You don't have to rate posts and you wont be looked down upon :) *

David, thanks for the troubleshooting ideas.  So far, we only know the noise appears on incoming calls transferred to someone else.  We did not test internal transfers or outbound call transfers.  I will test and let you know.


Using Cisco SPA 525g2 phones by any chance? If so you need to upgrade the phone firmware.



What firmware version did you upgrade to?

David Trad
Rising star

Hi Jason,

I know you have not come back to me with an update on the tests to see when this issue is happening, however the firmware version you should look at updating the SPA phones too is 7-4-8, i found this firmware also gets rid of a particular problem that I identified in the default one in the latest SW pack, delay in the DTMF transmission to the CUE, so an upgrade of the load should be done anyway.

Let us know once you have conducted the tests, or do the upgrade first and re-test everything again and then let us know of the results.



Cheers, David Trad. **When you rate a persons post, you are indicating a thank you or that it helped, but at the same time you are also helping to maintain the community spirit - You don't have to rate posts and you wont be looked down upon :) *

Hi Jason,

I think this is a G729 ab mixup.

On the incoming dial-peer from your SP, try adding the line

voice-class sip g729 annexb-all


It appears it was a problem with the 525 firmware.  Maybe it is fixed in 7.4.8 but all the STAC people are telling me not to load that firmware.

I swapped the 525 with a 504 running 7.4.8a and the problem is fixed.  They are not exactly a satifisfied customer since they paid for a 525 but it is a temporary solution until the 525 firmware gets straightened out.


I think they may be getting the firmware versions confused.  You should be able to upgrade the SPA525G phones to 7.4.8 without any issues in your case.

There were some problems found with 7.4.8 on the SPA50x phones, this is why 7.4.8a came out.  There is no 7.4.8a for the SPA525G phones as the issues they found is not present for these phones.

Current versions:

SPA525G - 7.4.8

SPA50xG - 7.4.8a

I know that was probably clear as mud, but I hope that helps to clear the confusion some.

Thank you,


I got this email from Adam Compton on 5/6/2011.

'In my eyes, right now 7.4.7 is the most stable version for the SPA525 phones.'

Another case I am working on, the tech said to load 7.4.4 for 525G and 7.4.6 for 525G2.  Maybe those two are reversed.  This issue is in regards to a SSL VPN phone issue. 

Basically, every tech we have spoken to has given us a different recommendation.  Even a level 2 tech has told us to use 7.4.7.  It seems like if you want to use the phone in the office, use firmware w.  If you want to use as a SSL phone, use firmware x.   If it is a 525G, use firmware y.  If it is a 525G2, use firmware z.

The 525s have really been problematic for us.   All we do is upgrade the phone firmware, downgrade the phone firmware, downgrade the IOS, upgrade, downgrade, etc.

I did some digging.   I support Darren's assertion.

However, there is an IOS Bug when using SPA525 with SSLVPN, where the headend (IOS ROuter) sends the phone an 'unknown packet received' message, causing the SPA525 to reset.  It is:

CSCtn53658 SPA525 phone reset after' Unknown packet received' message

The fix for this would be in IOS and there is no committed fix at this time.

If you have found a way to work around it by downreving the phone firmware so that the phone is more tolerant, perhaps thats what others are finding, and hence causing the confusion, not sure?

I am sorry I dont have more to share here.  I do run two SSL VPN SPA525s and do not see the issue, which makes me more compasionate for the TAC team since there may also be something more to this that what has already been disclosed as known.