@lasdisc , ANDY, It very well could be a dirty fan or a faulty fan. You can use the links below to assist in opening the computer to access the fan, heat sinks, board etc. and give the inside of the laptop a thorough cleaning as shown in the 1st link. 3rd link is your service manual. You should try to isolate where the noise is coming from before opening the laptop, by chance that it is not the fan. If fan is not spinning freely or you may just not trust it, maybe just replace it for piece of mind, Link #4 shows replacement fan, which you can also do a search on for better pricing perhaps. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
https://www.youtube.com/watch?v=ZT0ovCntxbs
https://www.youtube.com/watch?v=VvJwlTcpQOM
http://www.hp.com/ctg/Manual/c03591253.pdf?source=aw&aid=7169&jumpid=af_6mrc7uxaeb&awc=7169_1487119485_a5488e1d9f4ca2778a40c34717661eb6&AOID=35252&pbid=78888&siteid=Skimlinks
https://www.amazon.com/FEBNISCTE-dv7-7212nr-dv7-7223cl-dv7-7227cl-dv7-7230us/dp/B00VUD722A