I have found that when I am playing a whistle and drinking beer, as one does, low or high, when I burp whilst playing, the whistle pitch drops buy almost a tone.
Any ideas?
wiz
The CO2 in your eructation has different acoustic properties, just as helium does.
http://www.speech.kth.se/prod/publications/files/qpsr/1996/1996_37_4_037-043.pdf
And for those who do not imbibe alcoholic beverages, the same phenomenon can be observed with any carbonated soft drink.
It’d be a neat party trick if one could control the burps well enough to use the pitch drop as part of a tune.
And maybe we should inquire of the next new member that complains of their whistle playing flat just what beverage they were drinking when they made that observation. 
Feadoggie
It could be another kind of ornamentation, an alternative to the strike.
It generally has more to do with a “tap”.
I saw what you did, there.
Or perhaps something that is usable for those who complains of their whistle playing a bit too sharp… 
A true beer drinker can pick his spots. Word to the wise!
Guess we’re old enough to remember “Taprooms” here in PA!
And here I’ve been half holing those f nats all this time…
Conversely, the less CO2 in the beer, the flatter it becomes.
Isn’t that why Guinness has N2 instead of CO2? 
What if you’re more N2 Murphys than Guinness? I find it gives my belches more of a pure drop sound…