Bad noise or funny noise?

[GH85Carrera]

Today I changed the oil & filter in my 1985 Carrera with 125,000 miles. The old Mobil 1 (Extended performance) with about 500 miles on it went away and the new Swepco 15-40 went in. In the past I used the Mobile 1 silver cap oil.

I took a 30 minute drive to get things up to full temperature before I changed the oil. Everything was 100% normal. The magnetic plugs were nice and clean. It is strange to see purple oil but I trust what I have read on this site.

I started it up and everything sounded normal until I blipped the throttle. There was a new sound. It was a brrabrrabrrbrrabrrbrra that changed speed with the RPM. That is totally new. I have never heard that noise before. I moved the car from my work space to it's home space. It is a 3 car garage so it was not a long trip. I left the engine running and went to the engine compartment. As I changed the throttle the noise would increase. I turned off the engine and scratched my head. I put my other car back in it's normal space cleaned up some of the mess and scratched my beard. What was that noise? Strange noise, hmmmmm. I scratched several other body parts and drank a beer.

I have never been near a 911 when the chain tensioners are bad so I have never heard "the" failure noise. With a Carrera I have not been worried about chain tensioners. That is one reason I bought a Carrera!

5 minutes later I started my Carrera and the noise was gone. When it was there it sounded like it was coming from the distributor area. I took it out for a short trip through the neighborhood. There was no noise so I took a 10 minute drive. All was normal.

Tomorrow is the 1st autocross of the season in War Bonnet Region PCA. Our schedule is the 2nd Sunday of the month all year long. If the noise is gone when I start it in the morning I will autocross. I am real glad I don't have the Green Bay weather! WOW (that game is on right now.)

So now to the question, what do you think that noise could be? It is a bad pookie noise or something I can ignore for now.

[911s55]

The oil was probably recirculating through the cooling system

[GH85Carrera]

On Sunday morning I started the engine and all sounds were normal. It ran great all day at the autocross. It still runs great.

I am totally stumped as to what the sound was.

Any ideas?