Last year I bought a new Celestion Gold, to use with my Ceriatone Bluesmaster 50

As soon as it was installed, there was a problem
I used it running clean like a black-face fender twin sound, not at max volume - about halfway, and on certain notes it had a nasty raspy buzz.
I removed it from the cab, and laid it flat facing upwards on a carpeted floor, and it sounded the same.
It sounded the same with another clean amp too
It sounded fine except around the C (261Hz) on the D string and also C (131Hz) on the A string,
And then it rasped unless played quietly, even when all the treble is rolled off on the amp

I paid for it to be returned to Celestion (about £14). After a month, They sent another - this one sounded much better, with just a slight noise - but this got worse over time, so I called Celestion again

This speaker had a small problem when I got it, but it has gotten worse with time
Again I removed this speaker and tested it facing upwards, not mounted in a cab, 2-3 weeks ago, and got the same fault as when it was in the cab - rasping around E on the A string
However, I tested it again after 2 weeks, and the effect had lessened, after storage with the cone facing upwards for 2 weeks.
I have been told by someone  I respect that misalignments are exacerbated by the effects of gravity when the speaker is mounted normally (i.e. the cone pointing horizontally)
My assumption is that it had a slight fault, which has gotten worse with the effects of gravity over time

I paid £14 again for it to go again to Celestion.
The first response I got back from Celestion this time was:
"The speaker has been assessed in our quality department and I have been advised that there is nothing wrong with it and that some amps can cause this phenomena with the Celestion Gold and Blue speakers. We will ask our acoustic engineer to test it next week but unless he finds an fault I suggest you will have to have a credit if you are not happy with the speakers performance as a replacement will only be the same."

Does this sound very likely to anyone? Surely the only reason a speaker should rasp on certain notes when played clean is voice coil rub

Trouble is I love the sound of the Gold with this amp - I have found nothing as good. I have tried and EVM12
I have tried a Fane AXA12 and it's not quite as nice with the BM50. I could use a Tayden, but it's a special order to get a reinforced 50w one.
I thought about buying 4 unused pre-owned Celestion Golds I saw for sale and selecting the best, but the seller wanted £100 shipping (in the UK)

Any advice please?

I own 2 Golds and I think this speaker is the best speaker out there. Fortunately I have no issues with mine and I'm sorry to hear you have this thing with yours. A friend of mine just bought 50W Tayden for his Bluesmaster and I can't wait to hear how it stands up compared to my Celestion. He tells me it sounds warmer but I guess I need to hear it with my own ears.
Good luck...

That is my plan
I gave them a list of other speakers I have that work fine, to avoid being fobbed off too easily. I told them I love them, but want one that works.
I have a Weber Blue dog ceramic with doping, which is good, but not as nice as the Gold, I gather their pricier models are as good as anyone's though

Celestion have been excellent, they have sent me a new unit, which works perfectly, and another one free, as a gesture of goodwill (not tried that one yet).
I missed the sound of the Gold on my BM50 so much, my EVM12L is good with the BM50, just doesn't hit the perfect spot that the Gold can (the EVM is a little too shrill and scooped, and even when you correct it, the added colour from the Gold is not there)

(The EVM12L is much better for the OTS though, and my Twin II, they need less colour adding)

That's great to hear that celestial took care of you. Good customer service can be hard to find these days