"Mike Williams" wrote:

When the anomaly was first noticed, back in 1998, there were some whacky
suggestions put forth that gravity might not exactly follow an inverse-
square law, but that's been pretty well squashed by noticing that no
such effects have been observed on other probes such as Galileo and the
Voyagers. Whatever is causing the effect is specific to the design of
the Pioneer probes.

Voyager and Galileo are 3-axis stablized -- their thrustings would overwhelm
any equivalent 'Pioneer anomaly' signal.