Use a heatsink case instead of a case + heatsink + fan.
Most of my Pi 3B(+) computers are in generation 2 aluminum alloy Flirc cases, which act as a huge heatsink to keep the computer cool without the noise, additional power requirements or dust problems associated with fans. It even looks cool!
The second generation is made for the Pi 3B or 3B+ models and includes different thickness thermal pads for both. Note that recent production of the 3B has the taller SoC from the 3B+ (so use the thermal pad appropriate for the SoC). There is also an older model Flirc case for the Pi 1B+ and 2B models (they fit in the 2nd gen case, but you won't be able to see the power or activity LED).
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?