Test teams from all six MotoGP manufacturers took to the track at Sepang on Wednesday, to begin three days of fine-tuning ahead of the official test.

With no lap times available at private tests, the majority of interest was on any visual changes to the machines - especially with wings no longer allowed.

Having led the previous winglet development, Ducati has been the subject of much speculation over its 2017 fairing. Are they keeping the final design secret, having found a way to retain some of the lost downforce within the new rules?

Ducati Corse general manager Gigi Dall'Igna increased the intrigue by admitting the bike on display at last week's team launch would certainly change by the first race due to 'developments and optimisations'.

"We have 'something in the pocket'," he said.

But it wasn't the front of the GP17 that caused a stir at Sepang on Wednesday - it was the rear.

To be precise a new 'box' is now located under the tail unit, with the exhaust re-routed around the right-hand side of the structure, instead of being in the centre as previously.

So what is in the box and what is it for?

Is it related to the performance of the exhaust - a report on a Ducati 'jet exhaust' patent appeared only last week - or, at the other extreme, simply a storage unit for something like electronics. But if so, what has now taken their original place?

Crash.net asked test rider Michele Pirro about the new addition to his machine.

"It's to put salad inside... a hot dog... some coca cola... In case I get hungry after ten laps!" Pirro smiled.

Well, it was worth a try. It remains to be seen if the box appears on the machines of race riders Jorge Lorenzo and Andrea Dovizioso next week.

Both of Pirro's bikes had the new box fitted on Wednesday. One bike was a black, wingless, GP17 on which he spent most of his time. The other bike, also described as 'new', was painted in race colours, but still had 2016-spec wings.

The day began on a wet but drying track, with rain returning late in the afternoon. Pirro rode in both the dry and wet.

"It was strange conditions today, with the rain and it is difficult to completely dry this new asphalt. But it's okay. We start a new season today and our job was only to check if the new bike is okay. The control systems. And at this moment, no big problem.

"I rode the bike with no paint (black) on the fairing so there would be no damage if I fell! Maybe tomorrow I'll try the bike with wings. Tomorrow I'll continue with the shakedown, because it's an all-new bike. But the base is good. Casey will also be here tomorrow also."

Suzuki test rider Takuya Tsuda also put in substantial laps in the wet, an area of weakness for the GSX-RR last season, with new BSB signing Sylvain Guintoli also unafraid of the rain on the new GSX-R superbike.

Yoshimura has invited Guintoli, plus Suzuki's MotoAmerica riders Toni Elias and Roger Lee Hayden to help develop the new machine alongside factory test rider Nobu Aoki.

MotoGP and Superbike machines from Honda and Yamaha were also on track with Japanese test riders, while Mike di Meglio was at the controls of the Aprilia RS-GP and Mika Kallio the KTM RC16.

The private Sepang test continues on Thursday and Friday, with the official test - attended by all 2017 race riders - starting on Monday.

By Peter McLaren