What is this sound? Vintage Certina

[Leitemods]

Hi. I have an old Certina from ca. 1961 that I bought a few years ago. It has always had this loud, extra "tick" sound to it, and I'm not knowledgeable enough to know what causes it and if it's something I can correct or not. The movement's name is 28-15. When I've placed it on the timegrapher, the beat error is under 0.5ms and it runs well enough both on my wrist and on the machine. The only issue is this extra ticking sound, and it's so loud that I'm not really wearing the watch because of it.

If anyone can assist on what causes it and if it's a fairly easy thing to fix or too advanced for a beginner, that would be great!

Start with low volume!! The quality of the clip might not be very good. I've attached both an audio file and a link to an uploaded version of the clip. uploaded version

Thanks in advance.

tickingsound.mp3

[HSL]

This sound is very similar to overbanking but since it's so loud and out of beat it might even be the balance beating against the hairspring stud. But you probably will find the source to the sound somewhere around the balance. 

Edited January 29, 2019 by HSL

[Nucejoe]

I agree with HSL furthure, fork-impulse  interface as well,  which is fork horn hitting on the impulse jewel ( impact) while as the name roller implies , the horn is roll the impulse jewel into motion not bang on it, which produces  the  * ING*  sound that comes from HS. Such HS  resonations are not longitudinal like fourier sinsosoudal subfunctions. To invisige the source of the sound , HS is resonalting much like a guitar spring to produce  the * ING* vibrations.

This would have next to no effect on frequency and timekeeping of the watch. Sensatively we like to hear the pallets tic  to clear tic- toc music.