Facebook has again denied eavesdropping on conversations to target adverts, following persistent speculation on the part of users who have received suspiciously timed promotional messages.

Rob Goldman, the head of advertising at the social network, issued the denial in response to a question from the host of tech podcast Reply All. “I run ads product at Facebook. We don’t – and have never – used your microphone for ads. Just not true,” Goldman tweeted. He later added that the denial holds true for Facebook’s other social network, Instagram, as well.

The allegation that Facebook secretly spies on users to better profile them for advertising is long-running and hard to kill for the social network. The rumour appears to have started in May 2014 when the company launched a feature for its smartphone app called “Identify TV and Music”, which listens for ambient noise when a user is writing a status update.

If it hears a TV show or song that it recognises using the smartphone’s mic, it offers the user the option of automatically tagging that show or song in their status update, shaving a few seconds off the time it takes to share the info. Less than a month after the feature was launched, the company had to issue a denial that it was “always listening”.

But Facebook has also had to admit to occasionally running its smartphone app in the background when it shouldn’t be. In 2015, it fixed an issue that left it running a silent audio stream after the user had closed the app on an iPhone, meaning that the device’s battery life plummeted. “The app isn’t actually doing anything while awake in the background, but it does use more battery simply by being awake,” Facebook’s Ari Grant said at the time.

Another fact that has bolstered suspicions is that, since almost every Facebook user will have shot video or photos with it or Instagram at some point, or used Messenger to carry out a video or audio conversation, the app already has the permissions it would need to – hypothetically – carry out the eavesdropping.

The biggest fuel for the fire, however, is the sheer number of uncanny coincidences that many users have experienced. In the responses to Reply All, people described adverts for cat food after discussing getting a cat, for phone holders after expressing desire for them, and stating “so you popped the question!” minutes after a wedding proposal.

Facebook has never directly addressed the coincidences, but others have offered competing explanations, from effective targeting using the rest of the company’s vast hoard of data, to sheer weight of numbers: with 1.7 billion users being served tens of adverts a day, there’s always going to be something uncanny.