I am having a weird 1px line showing on my 2007/2010 Outlook emails.

I know there is an issue with Outlook 2016 that was solved on this thread:
https://litmus.com/community/discussions/4990-outlook-2016-1px-horizontal-lines-showing-up-in-the-body

This is what it looks like:
image

the line is showing right above the image and uder the product tile.

I am using this light gray background. I recently converted my td's to th's because I was having issues with Outlook IOS, and it seems that I started having issues with these horizontal lines since the conversion.

this is what my code looks like:
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tbody>
<tr>
<th style="padding-bottom: 32px; padding-top: 30px; background-color: #f5f5f5;">
<table width="100%" cellpadding="0" cellspacing="0" border="0">
<tbody>
<tr>
<th class="mobile-cell-stack" style="color: #64a70b; font-size: 24px; font-weight: bold; line-height: 24px; padding-bottom: 10px; padding-left: 30px; text-align: left;">
Save $250
</th>
</tr>
<tr>
<th class="mobile-cell-stack align-center padding-bottom-35" style="font-size: 18px; font-weight: normal; line-height: 22px; padding-bottom: 30px; padding-left: 30px; text-align: left; color: #666666;">
Product Title
</th>
</tr>
<tr style="line-height: 1px">

<th class="padding-bottom-30" style="padding-bottom: 50px; text-align: center;">
<img class="g-img" src="folder/img" width="250" height="205" alt="" border="0" style="vertical-align: middle; display: block;" />

</th>
</tr>
</tbody>
</table>
</th>
</tr>
</tbody>
</table>

But has anyone experience this behaviour and how did you fix it?